This is a research project grant (R01) application for Cardiac Biomarkers in Pediatric Cardiomyopathy. In this grant proposal, there will be three specific aims. The first will attempt to determine the clinical importance of established and novel cardiac biomarkers in children with newly diagnosed (incident) dilated cardiomyopathy. The second will aim to assess the clinical utility of cardiac biomarkers of collagen metabolism in determining the presence of myocardial fibrosis, as established by cardiac MRI, and diastolic dysfunction, as established by echocardiography in both newly diagnosed and existing cases of idiopathic or familial hypertrophic cardiomyopathy in children. The third and final aim will focus on determining whether longitudinal changes in cardiac biomarkers are associated with worsening heart failure class in clinically stable children with dilated or hypertrophic cardiomyopathy. These studies will significantly increase our understanding of pediatric cardiomyopathy, suggest new areas of research, and improve patient management as it relates to determining the most appropriate evidence-based clinical care for pediatric cardiomyopathy patients.